Measuring based on a vibrating sensor of angular velocity has proved to be a method of measuring angular velocity having a simple concept and being reliable. The principle of operation of vibrating sensors of angular velocity most often used is the so called tuning fork principle.
In a vibrating sensor of angular velocity, a certain known primary motion is produced and it is maintained in the sensor. The motion to be measured by means of the sensor is then detected as a deviation of the primary motion. In the tuning fork principle the primary motion is a vibration of two linear resonators vibrating in opposite phase.
An external angular velocity affecting the sensor in a direction perpendicular to the direction of motion of the resonators causes Coriolis forces influencing the masses in opposite directions. A Coriolis force proportional to the angular velocity is detected either directly from the masses, or the masses are connected on the same rotational axis, whereby the detection motion is angular vibration in the direction of the angular velocity axis.
Central features required of sensors of angular velocity are resistance to shaking and impact. Particularly in demanding applications, such as e.g. driving control systems in the car industry, these requirements are extremely tight. Even a sharp blow, like for instance an external impact caused by a stone, or the vibration caused by a car stereo should not influence the output of the sensor of angular velocity.
Prior art is described below with exemplifying reference to the accompanying figures, of which:
FIG. 1 shows a diagram of the functional structure of a vibrating micro-mechanical Z sensor of angular velocity according to prior art.
FIG. 2 shows a diagram of an exemplifying capacitive implementation of a vibrating micro-mechanical Z sensor of angular velocity according to prior art, and
FIG. 3 shows a diagram of the functional structure of a vibrating micro-mechanical X/Y sensor of angular velocity according to prior art.
FIG. 1 shows a diagram of the functional structure of a vibrating micro-mechanical Z sensor of angular velocity according to prior art. The depicted vibrating micro-mechanical Z sensor of angular velocity according to prior art comprises a mass 1, which is supported in the X axis direction to an excitation frame 2 by means of springs 4, 5. Said excitation frame 2 is further supported in the Y axis direction to a support structure 3 by means of springs 6, 7.
In the vibrating micro-mechanical Z sensor of angular velocity according to prior art, the mass 1 in the center and the excitation frame 2 surrounding it are activated into a primary motion in the Y axis direction, which occurs by means of the springs 6, 7 supported to the support structure 3. The detection axis, in the X axis direction, formed by means of the suspension 4, 5 supporting the mass 1 to the excitation frame 2, is perpendicular to the primary motion.
When the structure vibrating in the primary motion is turned in relation to the Z axis perpendicular to the surface plane, the mass 1, which is moving in the primary motion, experiences a Coriolis force in the direction of the X axis, perpendicular to its direction of motion. Then, further, the detection springs 4, 5, in addition to damping, determine the amplitude and phase of the vibration of the generated detection motion.
FIG. 2 shows a diagram of an exemplifying capacitive implementation of a vibrating micro-mechanical Z sensor of angular velocity according to prior art. In the depicted Z sensor of angular velocity, the common primary motion of the mass 1 and the excitation frame 2 is electrostatically activated by means of activation comb structures 8, and it is detected by means of detection comb structures 9. On the other hand, the secondary motion caused by the Coriolis force is differentially detected by means of capacitive comb structures 10, 11. Such a sensor is often made differential by coupling two structures, like the one described above, to each other, whereby a structure significantly more insensitive to external mechanical interference is achieved. One such sensor solution according to prior art is described i.a. in U.S. Pat. No. 6,752,017.
FIG. 3 shows a diagram of the functional structure of a vibrating micro-mechanical X/Y sensor of angular velocity according to prior art. The principle of such a sensor solution according to prior art is described i.a. in U.S. Pat. No. 5,377,544. The depicted vibrating micro-mechanical X/Y sensor of angular velocity according to prior art comprises a rotation mass 12, which is supported at the center to a support structure 13 by means of a suspension 14, 15. The vibrating micro-mechanical X/Y sensor of angular velocity according to prior art further comprises capacitive electrodes 18 provided above or below the rotation mass 12.
In the described vibrating micro-mechanical X/Y sensor of angular velocity according to prior art, the rotation mass 12 in the center is activated into a primary motion as a rotation movement in the surface plane around the Z axis by means of electrostatic excitation comb structures 16 and primary motion detection comb structures 17. The detection in the direction of the X/Y plane, formed by means of the support 13 and the suspension 14-15, is perpendicular to the rotation axis of the primary motion.
When the depicted vibrating micro-mechanical X/Y sensor of angular velocity according to prior art is turned in relation to the X axis, the Coriolis forces generate in the rotation mass 12, in phase with its speed, a torsion moment in relation to the Y axis, which torsion moment by means of the spring 14 generates a torsion vibration in the rotation mass 12. Correspondingly, when the X/Y sensor of angular velocity is turned in relation to the Y axis, the Coriolis forces generate in the rotation mass 12, in phase with its speed, a torsion moment in relation to the X axis, which torsion moment by means of the spring 15 generates a torsion vibration in the rotation mass 12. The generated vibrations can be capacitively detected by means of the electrodes 18.
For a multitude of applications in consumer electronics, a sensor of angular velocity of extremely small size and cost efficiency is needed. Measuring in several degrees of freedom is challenging in sensors of angular velocity, since often both activation and detection in more than one degree of freedom are required. In particular, a cost effective implementation in one component for measuring angular velocity in relation to an axis in the surface plane and in relation to an axis perpendicular to the plane, has proved to be a challenge.
Cost effectiveness in sensors of angular velocity is determined, in addition to the surface area, also by the complexity of the electronics required for the element. The activation motion occurring in several degrees of freedom in the measuring resonators for different axes is perhaps the biggest single factor increasing the surface area and the complexity of the electronics.
The object of the invention is then to achieve a structure of a vibrating sensor of angular velocity suitable for a small size, by means of which angular velocity can be measured in two or three degrees of freedom utilizing a common activation motion.